Method of forming green part and manufacturing method using same

ABSTRACT

A method of manufacturing a part, including providing a green body made of powder injection molding material and connected to a solid support member partially contained in the green body. The support member is engaged with a retaining fixture of a machine tool. While supporting the green body through the engagement between the support member and the retaining fixture, the green body is machined to obtain a machined green part. The machined green part is debound and sintered. A method of forming a powder injection molding part in a green state including machining a molded body using a machine tool while supporting the blank with a retaining fixture, and a machining blank having a green body and a solid support member including one locating feature of a pair of complementary locating features snuggly engageable with one another are also discussed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/479,738 filed Sep. 8, 2014, which claims priority on United StatesProvisional Application No. 62/026,989 filed Jul. 21, 2014, the entirecontents of both of which are incorporated herein by reference.

TECHNICAL FIELD

The application relates generally to powder injection molding and, moreparticularly, to green part(s) obtained by powder injection molding.

BACKGROUND OF THE ART

Powder injection molding such as metal injection molding may offer acost-savings advantage on small, complex parts that are difficult tomachine. However, the process to design the mold for a given workpieceis often iterative, for example because of difficulties in predictingthe amount of shrinkage during the debinding and sintering steps; assuch, it may be required to successively manufacture and test severalmolds before the dimensions for the final mold can be determined.Accordingly, design, manufacture, and test of a mold can lead tosignificant lead-time initial cost.

SUMMARY

In one aspect, there is provided a method of manufacturing a part, themethod comprising: providing a green body made of powder injectionmolding material, the powder injection molding material including asolidified binder and a powder material mixed with the binder, the greenbody being connected to a solid support member partially contained inthe green body; engaging the support member with a retaining fixture ofa machine tool; while supporting the green body through the engagementbetween the support member and the retaining fixture, machining thegreen body using the machine tool to obtain a machined green part; anddebinding and sintering the machined green part.

In another aspect, there is provided a machining blank comprising: agreen body made of powder injection molding material, the powderinjection molding material including a solidified binder and a powdermaterial mixed with the binder; and a solid support member having agreater rigidity than the green body, the support member having an innerportion embedded within the green body and an outer portion extendingout of the green body, the outer portion including one feature of a pairof complementary locating features snuggly engageable with one another,the outer portion being adapted to be engaged with a retaining fixtureincluding the other feature of the pair of complementary locatingfeatures.

In a further aspect, there is provided a method of forming a powderinjection molding part in a green state, the method comprising:providing a blank having a molded body, the molded body being in thegreen state and made of powder injection molding material, the powderinjection molding material including a solidified binder and a powdermaterial mixed with the binder material; engaging the blank with aretaining fixture of a machine tool; and while supporting the blank withthe retaining fixture, machining the molded body using the machine toolto obtain a machined green part in the green state.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic, cross-sectional tridimensional view of a moldincluding a support member in accordance with a particular embodiment;

FIG. 2 is a schematic, exploded tridimensional view of the mold of FIG.1 and of a green body molded therein, with a support member partiallybroken away to show an underlying portion of the green body, inaccordance with a particular embodiment;

FIG. 3a is a schematic tridimensional view of the green body and supportmember of FIG. 2 retained in a machine tool;

FIG. 3b is a schematic tridimensional view of a green body in accordancewith another particular embodiment, in a support member similar to thatof FIG. 2, retained in a machine tool;

FIG. 3c is a schematic tridimensional view of the green body and supportmember of FIG. 3a during machining;

FIG. 4 is a schematic, cross-sectional tridimensional view of a moldincluding a support member in accordance with another particularembodiment;

FIG. 5 is a schematic, cross-sectional tridimensional view of thesupport member engaged to a green body molded in the mold of FIG. 4;

FIG. 6a is a schematic tridimensional view of the green body and supportmember of FIG. 5 retained in a machine tool; and

FIG. 6b is a schematic tridimensional view of the green body and supportmember of FIG. 6a during machining.

DETAILED DESCRIPTION

The present application discusses a method of manufacturing a part usingpowder injection molding, in which the green part is machined afterbeing molded and before the debinding and sintering steps are performed.

As is typical in powder injection molding, a suitable feedstock isinjected into a mold cavity to obtain the green part. Such a feedstockcan include high temperature resistant powder metal alloys (metalinjection molding), such as a nickel superalloy, or ceramic, glass,carbide powders or mixtures thereof, mixed with an appropriate binder.Other high temperature resistant material powders which may include onematerial or a mix of materials could be used as well. The feedstock is amixture of the material powder and of a binder which may include one ormore binding material(s). In a particular embodiment, the binderincludes an organic material which is molten above room temperature (20°C.) but solid or substantially solid at room temperature. The binder mayinclude various components such as surfactants which are known to assistthe injection of the feedstock into mold for production of the greenpart. In a particular embodiment, the binder includes a mixture ofbinding materials, for example including a lower melting temperaturepolymer, such as a polymer having a melting temperature below 100° C.(e.g. paraffin wax, polyethylene glycol, microcrystalline wax) and ahigher melting temperature polymer or polymers, such as a polymer orpolymers having a melting temperature above 100° C. (e.g. polypropylene,polyethylene, polystyrene, polyvinyl chloride). Different combinationsare also possible. In a particular embodiment, the material powder ismixed with the molten binder and the suspension of injection powder andbinder is injected into the mold cavity and cooled to a temperaturebelow that of the melting point of the binder. “Green state” or “green”as discussed herein refers to a molded part produced by the solidifiedbinder that holds the injection powder together.

Since the feedstock is wax and/or polymer based, machining the greenpart can be performed with cutting feeds and speeds that are higher andcutting forces that are lower than typical feeds, speeds and forces forthe machining of solid metal (for example the same metal as that foundin powder form in the green part), and even when compared with “soft”metals such as aluminum. In a particular embodiment, a machine tool thatis designed for machining wax and plastics (e.g. small desktop CNCmilling machine) is used to machine the green part. In a particularembodiment, the cutting feeds and speeds are similar to that used duringthe machining of wax. In a particular embodiment, the metal powderpresent in the green part provides for an increased materialconductivity when compared to the binder material alone, which may helpdissipate heat that may be generated during machining.

In a particular embodiment, the method may be used for therapid-prototyping of powder injection molding parts, for example toobtain a part for tests. This may allow the final part to bemanufactured within a timeline in the order of days rather than months,allowing for quicker manufacture of parts available for testing. Forexample, shrinkage and deformations of the part until the end of thesintering process can be observed and measured, and a new green partwith different dimensions can be produced by machining if the desiredfinal dimensions are not obtained. Iterations in the green part designcan thus be done by machining rather than by mold modifications, whichin a particular embodiment significantly reduces the development timeand development cost for the part. Once the final design has beenconfirmed, a mold can be ordered for mass production.

The green part may be molded with an integral solid support member whichis used to support the part during the machining process. An example ofa mold and support member in accordance with a particular embodiment isgenerally and schematically shown in FIGS. 1-2. In this embodiment, themold 20 includes a plurality of mold elements which together define amold cavity 22 having a substantially prismatic shape to define asubstantially prismatic green body 50. The mold elements include abottom plate 24, the support member 26 resting against the bottom plate,an intermediary element 28 resting against and on top of the supportmember 26, and a top plate 30 resting against and on top of theintermediary element 28. The top surface 32 of the bottom plate 24 andthe bottom surface 34 of the top plate 30 both border the mold cavity22. The intermediary element 28 and an outer portion 36 of the supportmember 26 both have similar hollow rectangular shapes defining a closedperimeter having an inner surface 38, 40 bordering the mold cavity 22.Although not shown, additional intermediary elements can be used to varythe shape of the green blank; for example, an intermediary element maybe received within the support member 26 to close part of the areadefined within the support member 26, such as to define a smaller greenbody 50 a as shown for example in FIG. 3b . Additional element(s) mayalso be added above and/or below the support member 26. Alternately, theintermediary element 28 may be omitted, for example to obtain a thinnergreen body. Other configurations are also possible.

The mold elements 24, 26, 28, 30 are interconnected to enclose the moldcavity 22. In the embodiment shown and with reference to FIG. 2, thisconnection is defined by two corner pins 42 extending upwardly fromopposed corners of the bottom plate 24 and received in correspondingaligned holes 44 defined through the other mold elements 26, 28, 30. Itis understood that the number and configuration of the mold elements mayvary, as long as they create the desired shape for the mold cavity andcan be disassembled for removal of the molded part without damaging it.

Referring back to FIG. 1, it can be seen that the support member 26 alsoincludes an inner portion 46 protruding from the outer portion 36 intothe mold cavity 22, in the form of a plurality of tabs extendinginwardly from the inner surface 38. The inner portion 46 is shaped suchas to be gripped and retained within the green body 50 after the minimalshrinkage (e.g. 0.5 to 2%) that typically occurs as the bindersolidifies after molding. In the particular embodiment shown, the tabsof the inner portion 46 extend perpendicularly from the inner surface 38to define complementary grooves 48 in the green body 50 (FIG. 2), whichcompress the tabs as the green body 50 shrinks to lock each tab into itsrespective groove 48.

After molding, the green body 50 and support member 26 engaged theretoare removed from the mold cavity 22 and disengaged from the other moldelements 24, 28, 30, as shown in FIG. 2. In the embodiment shown, amachining blank 52 includes the green body 50 and the support member 26.The green body 50 is made of the mix of solidified binder and powdermaterial, and accordingly is rigid enough to be able to maintain itsshape and for some manipulation. The support member 26 has its innerportion 46 embedded within the green body 50 and its outer portion 36extending out of the green body 50 and surrounding its perimeter. Thesupport member 26 is made of a solid material having a greater rigiditythan that of the solidified green body 50 after molding. In a particularembodiment, the support member 26 is made of the same material as theother mold elements 24, 28, 30; alternately, different materials may beused. An example of a suitable material includes, but is not limited to,solid metal such as hardened steel.

Referring to FIG. 3a , the support member 26 is engaged with a retainingfixture 54 of the machine tool 56, such as to retain the blank 52 formachining of the green body 50. In a particular embodiment, the outerportion 36 of the support member 26 includes one feature 58 (FIG. 2) ofa pair of complementary locating features snuggly engageable with oneanother, with the other feature of the pair being defined in theretaining fixture 54 of the machining tool 56. In the embodiment shown,the feature 58 of the outer portion 36 is a male locating feature suchas a locating pin extending from the outer portion 36 away from thegreen body 50, and it is snuggly engaged within a corresponding femalefeature, e.g. locating hole, defined in the machine tool's retainingfixture 54. More than one pair of locating features may be used and/orthe configurations of the locating features may vary, but are configuredto allow for the support member 26 to be engaged to the retainingfixture 54 with a known location for the machine tool 56. In theembodiment shown, the outer portion 36 further includes a locating hole57 (FIG. 2) engaging a tailstock 59 (FIG. 3a ) of the retaining systemof the machine tool 56.

Referring to FIG. 3c , the green body 50 is then machined using themachine tool 56 while the blank 52 is supported through the engagementbetween the support member 26 and the retaining fixture 54, until thedesired shape defining the machined green part 50′ is obtained. In aparticular embodiment, the retaining fixture 54 maintains the blank 52in a fixed position during machining by a moving tool, e.g. a CNCmilling machine. In another embodiment, the retaining fixture 54 ismovable, for example to reposition (e.g. pivot) the blank 52 betweenmachining steps, and/or to move the blank 52 during machining. In aparticular embodiment, machining includes performing a first machiningoperation, then disengaging the support member 26 from the retainingfixture 54 and re-engaging them in a different relative position and/ororientation before performing another machining operation using the sameor a different tool. The complementary locating features on the supportmember 26 and retaining fixture 54 allow for the location of the greenbody 50 to be determined during the machining operations.

In the embodiment shown, the green body 50 is machined to produce themachined green part 50′ having the desired shape and a retaining portion50″ engaged to the support member 26 and connected to the machined greenpart 50′. The machined green part 50′ remains connected to the supportmember 26 only through its connection with the retaining portion 50″,defined here by a plurality of tabs 51. Accordingly, the support member26 is disengaged from the machined green part 50′ by breaking theconnection between the machined green part 50′ and the retaining portion50″, either manually or through the machining process.

In a particular embodiment, the support member 26 is freed from thegreen body, cleaned and re-used in the molding and machining of anothergreen part.

The machined green part 50′ is then submitted to a debinding operationto remove most or all of the binder. The green part can be debound usingvarious debinding solutions and/or heat treatments known in the art, toobtain a brown part. After the debinding operations, the brown part issintered. The sintering operation can be done in an inert gasenvironment, a reducing atmosphere (H₂ for example), or a vacuumenvironment depending on the composition of material to be obtained. Ina particular embodiment, sintering is followed by a heat treatment alsodefined by the requirements of the material of the finished part. Insome cases, it may be followed with hot isostatic pressing (HIP).Coining may also be performed to further refine the profile of the part.It is understood that the parameters of the sintering operation can varydepending on the composition of the feedstock, on the method ofdebinding and on the configuration of the part.

In another particular embodiment, the support member 26 remains engagedto the machined green part 50′ during debinding.

An example of a mold and support member in accordance with anotherparticular embodiment is generally and schematically shown in FIG. 4. Inthis embodiment, the mold 120 includes two mold elements 124 (only oneof which is shown, the other being a mirror image thereof) whichtogether define a mold cavity 122 having a substantially cylindricalshape to define a substantially cylindrical green body 150 (FIG. 5).Each mold element 124 defines one-half of the mold cavity 122 withopposed semi-circular wall surfaces 132, 134 interconnected by anarcuate inner wall surface 140 bordering the cavity 122. The moldelements 124 are interconnected to enclose the mold cavity 122. It isunderstood that the number and configuration of the mold elements mayvary, as long as they create the desired shape for the mold cavity andcan be disassembled for removal of the molded part without damaging it.

The support member 126 is made of solid material having a greaterrigidity than that of the solidified green body 150 and is in the formof a shaft, including an outer portion 136 extending out of the moldcavity 122 and an inner portion 146 extending from the outer portion 136into the mold cavity 122. In this embodiment, the mold cavity 122 and assuch the green body 150 molded therefrom, as well as the support member126, have a common axis of axisymmetry 160. This configuration may thusbe particularly suitable for use with a machine-tool of the turning type(e.g. turning lathe or mill-turn machine).

The inner portion 146 of the support member 126 is shaped such as to begripped and retained within the green body 150 after the shrinkageoccurring during solidification. In the embodiment shown, the innerportion 146 has an annular groove 162 defined in its outer surface, inwhich the material of the green body 150 engages to form a complementarylip 164 (FIG. 5). The inner portion 146 also includes a series ofprotruding teeth 166 in which the material of the green body 150 engagedto form complementary teeth (not shown) to form an anti-rotation lockingfeature. Shrinkage of the green body 150 during solidification tightensthe fit between the lip 164 and groove 162 and between the teeth 166 toengage the support member 126 to the green body 150. The green body 150and support member 126 engaged thereto are removed from the mold cavity122 and disengaged from the mold elements 124, as shown in FIG. 5, toform the blank 152.

Referring to FIG. 6a , the support member 126 is then engaged with aretaining fixture 154 of the machine tool 156, such as to retain theblank 152 for machining. Complementary locating features may be providedin the retaining fixture 154 and outer portion 136 of the support member126, such as for example a locating pin 158 (FIG. 5) extending from theouter portion 136 for snug engagement in a complementary locating hole(not shown) in the retaining fixture 154.

Referring to FIG. 6b , the green body 150 is then machined using themachine tool while the blank 152 is supported through the engagementbetween the support member 126 and the retaining fixture 154, until thedesired shape defining the machined green part 150′ is obtained. In theembodiment shown, the retaining fixture 154 rotates the blank about itscentral axis 160 while it is being machined by a moving tool. Themachining may include performing two or more machining operations, anddisengaging/re-engaging the support member 126 from the retainingfixture 154 between the machining operations. A face 129 of the supportmember 126 may be used as reference for locating of the blank 152between set ups and/or additional features may be included in thesupport member 126 to facilitate location of the blank 152, such as forexample a flat reference surface 127.

In the embodiment shown, the machining is performed to obtain themachined green part 150′ having the desired shape for the element to beproduced, and a retaining portion 150″ engaged to the support member 126and connected to the machined green part 150′. The machined green part150′ remains connected to the support member 126 only through itsconnection with the retaining portion 150″. Accordingly, the supportmember 126 is disengaged from the machined green part 150′ by breakingthe connection between the machined green part 150′ and the retainingportion 150″, either manually or through the machining process. Themachined green part 150′ is then debound and sintered.

In particular embodiment, the support member 126 is then cleaned byremoving the green material remaining connected thereto (e.g. bydestroying the retaining portion 150″), and re-used in the molding andmachining of another green part.

Although in the embodiments shown the molded green body 50, 150 isdepicted as a block shape, i.e. having none of the features of thedesired final shape for the part which are thus all obtained bymachining, it is understood that in other embodiments the green body maybe molded having some of the features of the desired final shape suchthat only part of the green body is machined, or with an intermediateshape between the block shape and the desired final shape, for example arough shape approximating and larger than the desired final shape. Themethod may also be used to perform secondary machining operations onmolded parts in the green state, including the removal of gates createdby the molding process, testing new/modified features on already moldedparts (as opposed to directly molding the modified part using anew/modified mold), and machining difficult to mold features with easierto mold features being directly obtained in the molding step.

The method may be used to shape any type of part that may be obtained bya metal or powder injection molding process, including, but not limitedto, gas turbine engine elements such as pieces of fuel nozzles,combustor panels, brackets, vanes, vane segments, vane rings, heatshields, combustion air swirlers, shroud segments, bosses, flanges, tubefittings, adaptors, airfoils, blades, levers, etc.

The shape of the support member 26, 126 may vary and is selected basedon the machine tool used and on the configuration of the green body tobe machined.

In some embodiments, the configuration of the green body and/or theproperties of the feedstock and/or the machining operations to beperformed allow for the green body to be sufficiently resistant to bedirectly supported during the machining operation(s), and accordinglythe support member is omitted.

It is understood that the machined green part 50′, 150′ may be assembledto one or more other green part(s) (whether machined or directly moldedto shape) prior to debinding, and these parts may be assembled in theirgreen state, connected using any type of suitable non-detachableconnections or detachable connections, and debound and sintered to fusethem together to form the final element. In a particular embodiment, theparts are fused during the debinding step. Alternately, the parts arejoined after the debinding step and prior to the sintering step.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Modifications other than those specifically described above which fallwithin the scope of the present invention will be apparent to thoseskilled in the art, in light of a review of this disclosure, and suchmodifications are intended to fall within the appended claims.

1. A machining blank comprising: a green body made of powder injectionmolding material, the powder injection molding material including asolidified binder and a powder material mixed with the binder; and asolid support member having a greater rigidity than the green body, thesupport member having an inner portion embedded within the green bodyand an outer portion extending out of the green body, the outer portionincluding one locating feature of a pair of complementary locatingfeatures snuggly engageable with one another, the outer portion beingadapted to be engaged with a retaining fixture including the otherlocating feature of the pair of complementary locating features.
 2. Theblank as defined in claim 1, wherein the support member is made of solidmetal.
 3. The blank as defined in claim 1, wherein the one locatingfeature is a locating pin protruding from the outer portion.
 4. Theblank as defined in claim 1, wherein the outer portion of the supportmember surrounds a perimeter of the green body, and the inner portionincludes a plurality tabs protruding inwardly from the second portioninto the green body.
 5. The blank as defined in claim 1, wherein thesupport member and the green body have a common axis of axisymmetry, thesupport member defining a shaft.
 6. A method of forming a powderinjection molding part in a green state, the method comprising:providing a blank having a molded body, the molded body being in thegreen state and made of powder injection molding material, the powderinjection molding material including a solidified binder and a powdermaterial mixed with the binder material; engaging the blank with aretaining fixture of a machine tool; and while supporting the blank withthe retaining fixture, machining the molded body using the machine toolto obtain a machined green part in the green state.
 7. The method asdefined in claim 6, wherein providing the blank includes molding themolded body by injecting a feedstock of the powder injection moldingmaterial into a mold cavity containing an inner portion of a solidsupport member to connect the inner portion with the molded body, andremoving the connected molded body and support member from the moldcavity, and wherein engaging the blank with the retaining fixture of amachine tool is performed by engaging an outer portion of the supportmember with the retaining fixture, the machining being performed whilesupporting the blank through the engagement between the outer portion ofthe support member and the retaining fixture.
 8. The method as definedin claim 7, further comprising disengaging the support member from themachined green part.
 9. The method as defined in claim 8, wherein:machining the molded body is performed to obtain the machined green partand a retaining portion engaged to the inner portion of the supportmember and connected to the machined green part; after the machining,the machined green part remains connected to the support member onlythrough the retaining portion; and disengaging the support member fromthe machined green part is performed by separating the machined greenpart from the retaining portion.
 10. The method as defined in claim 6,wherein engaging the blank with the retaining fixture maintains themolded body in a fixed position during the machining.
 11. The method asdefined in claim 6, wherein machining the molded body includes rotatingthe blank with the retaining fixture.